Also check the user manual of your display to see what resolutions and frequencies it supports.

Once you have connected the display to the HDMI port on the Elgato Thunderbolt™ 2 Dock, you can find out the frequencies and resolutions supported by your Mac and your display by going to System Preferences > Displays window. To view all the resolutions supported by your Mac, press the Option key and then press the Scaled option.